Parto Azmoon Azar
Engineering & Inspection Co.
‫شرکت مهندسی پرتو آزمون آذر‬
Peyman Rostami
peymanrostami@hotmail.com
Education:
B.Sc. Applied Physics - Nuclear (1989 - 1993)
Amirkabir University of Technology – Tehran
M.Sc. Nuclear Engineering (1995 - 1997)
Amirkabir University of Technology – Tehran
Certification:
1. ASNT NDT Level III – UT
2. ASNT NDT Level III – RT
3. ASNT NDT Level III – MT
4. ASNT NDT Level III – PT
5. Certified as “Radiation Protection Officer - RPO” from Iran Nuclear Regulatory
Authority (INRA) as the Iranian Authority for Radiation Protection,
2
Corrosion Under Insulation (CUI) and Fireproofing (CUF)
Inspection Techniques
According to: API Recommended Practice 583
First Edition, May 2014
By: Peyman Rostami
Parto Azoon Azar Engineering & Inspection Co.
3
Sphere collapse due to Corrosion Under Fireproofing (CUF)
4
Corrosion Under Insulation (CUI)
5
Introduction to Corrosion Under Insulation (CUI)
Corrosion under insulation (CUI) is one of the most well-known phenomena in the
process industries, and yet it still makes up an inordinately large percentage of
global maintenance expenditures.
CUI is a subject that is well researched and understood; extensive studies have been
commissioned to determine the causes, effects, prevention, and mitigation of CUI.
In the simplest terms, CUI is any type of corrosion that occurs due to moisture
buildup on the external surface of insulated equipment.
If undetected, the results of CUI can lead to the shutdown of a process unit or an
entire facility, and in rare cases it may lead to a process safety incident.
6
In almost every manufacturing and process industry, one of the most critical and
vulnerable components is the piping system,
7
External corrosion of carbon steel piping, pressure vessels and structural
components resulting from water trapped under insulation in conjunction with other
variables that accelerate and drive the corrosion,
8
External Chloride Stress Corrosion Cracking (ECSCC) of austenitic and duplex
stainless steel under insulation with other variables present, accelerate the corrosion,
9
Most of the insulation defects are associate with pipelines and vessels occur through
poor initial installation or subsequent damage to the insulation material during its
lifetime. Damaged insulation will allow water to saturate the materials nearest to the
metal where corrosion will eventually begin to occur.
10
Corrosion Under Fireproofing (CUF):
Corrosion of piping, pressure vessels, and structural components resulting from
water trapped under fireproofing,
Corrosion Under Insulation (CUI):
External corrosion of carbon steel piping, pressure vessels, and structural
components resulting from water trapped under insulation. ECSCC of austenitic and
duplex stainless steel under insulation is also classified as CUI damage,
When moisture penetrates insulation and fireproofing systems, the surface of the
underlying component will be subjected to corrosion,
11
CUI Failure of 4” Gas Compressor Recycle Line
Failure of Sphere Legs Due to CUF
CUI at an Insulation Support Ring
CUI and CUF are
phenomenon's that has
plagued the Oil, Gas
and Chemical Industry
for years,
12
Piping system externally maybe subjected to:
•
•
•
•
•
External forces of vibration,
Pipe support friction and wear,
Fatigue,
Climate condition,
Corrosion Under Insulation (CUI),
Piping system internally maybe subjected to:
•
•
•
•
•
•
Excessive pressure and/or temperature extremes,
Liquid or Vapor caused erosion,
Flow-accelerated corrosion,
Preferential corrosion in the heat affected zone of welds,
Localized pitting due to any number of causes,
Internal blockage,
13
CUI and CUF can be hard to find, identifying where to start is Key:
• Areas exposed to mist overspray from cooling water towers,
• Areas exposed to steam vents,
• Carbon steel piping systems insulated for personnel protection, operating between -12°C
and 175°C,
• Carbon steel piping systems that normally operate in-service above 175°C but are
intermittent service,
• CUI is particularly aggressive where operating temperatures cause frequent or
continuous condensation and re-evaporation of atmospheric moisture,
• Dead legs and attachments that protrude from insulated piping and operate at a
temperature different than the active line,
14
CUI and CUF can be hard to find, identifying where to start is Key:
• Austenitic stainless steel piping systems operating between 60°C and 205°C
(susceptible to ECSCC),
• Vibrating piping systems that have a tendency to inflict damage to insulation
jacketing providing a path for water ingress,
• Steam traced piping systems that can experience tracing leaks, especially at tubing
fittings beneath the insulation,
• Piping systems with deteriorated insulation, coatings and/or wrappings,
• Piping systems susceptible to physical damage of the coating or insulation, thereby,
exposing the piping to the environment,
15
Inspection for CUI and CUF Damages
According to API-583 (2014)
16
General:
The purpose of the insulation on equipment and piping should be well understood
before performing CUI inspections. This can help:
-
To establish priorities,
Determine what hazards may exist,
Determine if insulation can be removed while equipment / lines are in operation,
Determine if insulation can be permanently removed,
In fact, one of the big benefits from this insulation evaluation process is that it can
actually discover many areas do not really require insulation so permanent removal
results in 100 % elimination of CUI risk.
17
Inspection Methods and Techniques for CUI and CUF:
There are both direct inspection methods and indirect inspection methods for
detecting surface corrosion damages (caused by CUI or CUF) on equipment or
structural supports,
Direct Inspection Methods:
Direct inspection methods are classified as inspection methods conducted without
the presence of a protective barrier (insulation or fireproofing system),
In-Direct Inspection Methods:
Indirect inspection methods are classified as inspection methods conducted with
the protective barrier (insulation or fireproofing system) still in place,
18
In-Direct Inspection Methods:
A. Semi-Quantitative Methods:
These are inspection methods that indirectly quantify the relative degree of surface
corrosion that has occurred.
B. Qualitative Methods:
These are inspection methods that attempt to assess the quality of the insulation /
fireproofing system as an indirect measure of the potential for surface corrosion
damage.
These methods are conducted without removing the insulation or fireproofing from
the equipment or structural support.
19
1.
Direct Inspection Methods:
A. Visual Examination Method (VT) with Complete Removal of Insulation/Fireproofing
B. Liquid Penetrant Examination Method (PT)
2.
In-Direct Inspection Methods:
A. Semi-Quantitative Methods:
1. Guided Wave Examination Method (GWT)
2. Radiographic Examination Methods:
a) Tangential Radiographic Inspection (Profile radiography)
b) Double Wall Radiographic Inspection (Film Density Measurement Technique)
c) Radiometric Profiling
d) Real-Time Radiographic Examination Method (RTR)
e) Computed and Digital Radiography Testing:
i. Computed Radiography (CR)
ii. Digital Radiography (DR)
3. Pulsed Eddy Current Method (PEC)
B. Qualitative Methods:
a) Visual Examination Method (VT) with Partial Removal of Insulation
b) Neutron Backscatter Examination Method
c) Thermal/Infrared Imaging Examination Method
20
Visual Inspection (VT)
21
Visual Inspection (VT):
• Visual Inspection (VT) of Piping / Equipment can serve as a “Base-Line” to help
establish a plan of action and path forward,
• Two basic types of Visual Inspection (VT) examinations:
1. Visual Inspection with Complete Removal of Insulation/Fireproofing,
2. Visual Inspection with Partial Removal of Insulation/Fireproofing,
22
Visual Inspection (VT) with Complete Removal of Insulation:
The most reliable method to detect CUI and CUF on carbon and low alloy steel
systems is to physically remove the insulation or fireproofing and visually inspect
the surface for damage.
This approach is costly since insulation or fireproofing on equipment or structural
supports has to be stripped and reinstalled.
Scaffolding costs to access insulated areas being inspected can be significant
especially for large vessels or piping systems on columns or towers.
Scaffolding costs can be reduced in some situations utilizing rope access-qualified
inspectors.
23
Visual Inspection (VT) with Complete Removal of Insulation:
Advantages:
• Only method that can detect 100 % of all surface corrosion damage,
• Eliminates any misinterpretation,
Disadvantages:
• Expensive to remove and reinstallation of insulation on equipment or structural
components,
• May require additional funds and time for scaffolds,
• Process problems may occur if the insulation is removed while the piping is in
service,
• Inspection personnel need to be careful to avoid contact with surfaces at or above
60 °C,
• Special precautions are necessary on asbestos insulated systems,
24
Visual Inspection (VT) with Partial Removal of Insulation:
The most reliable technique to detect CUI is to physically remove the insulation and
visually inspect the surface of the vessel or piping. This approach is costly since
equipment must be de-insulated and re-insulated and frequently requires scaffolding
to access areas for inspection.
Removing smaller sections of insulation (windows) is useful for advanced
inspections to help prioritize equipment for remediation or more thorough follow-up
inspections.
The placement and size of these inspection windows is very important.
25
Windows should be cut where CUI is most likely as following “key areas”:
1. At poorly sealed insulation,
2. At low points in the piping system where water can collect,
3. Damaged areas of insulation,
4. Insulation termination points,
5. Protrusions of Punctures,
6. Damaged seals,
7. At insulation support rings or vessel stiffening rings,
8. At areas where the insulation jacketing is in poor condition and water can
penetrate the insulation system,
The areas where insulation is removed (windows) should be large enough to be
representative of the condition of the equipment,
It may be necessary to cut several windows in suspect locations because of the
difficulty in predicting where CUI damage has occurred,
26
Visual Inspection (VT) with Partial Removal of Insulation:
Advantages:
• Costs associated with insulation removal / reinstallation are significantly reduced
compared to complete removal of insulation,
• Limited exposure to hot surfaces for personnel,
Disadvantages:
• CUI damage can be missed since only a limited area of the equipment is inspected,
• Special precautions are necessary on asbestos insulated systems,
• Windows cut in insulation pose a potential leak path for water ingress if insulation
not effectively repaired/sealed,
27
Liquid Penetrant Examination (PT)
28
Liquid Penetrant Examination Method (PT):
Typically, ECSCC on insulated stainless steel equipment is not normally detected
until leakage occurs,
When this occurs, inspection of the area using PT is an effective way of determining
the extent of damage (cracking) on austenitic and duplex stainless steel. Damage is
often associated with the weld heat affected zone (HAZ),
Liquid penetrant testing is generally limited to surface temperatures below 49 °C,
29
Liquid Penetrant Examination Method (PT):
30
Liquid Penetrant Examination Method (PT):
Advantages:
• Capable of detecting very small discontinuities,
• Relatively inexpensive non-sophisticated equipment,
Disadvantages:
• Surfaces have to be clean and free of organic or inorganic contaminants that can
impede the action of the penetrating media,
• When sprayed, penetrants are easy to ignite when exposed to ignition sources,
• Cold surfaces require longer dwell times to allow sufficient time for penetrant to
be drawn into the crack,
31
Neutron Backscatter Method
32
Neutron Backscatter Method:
Am241/Be
Half Life: 432 Years
Primary Emission: Neutron
Primary Energy: 2-10 MeV
33
Neutron Backscatter Method:
The neutron backscatter technique works because of the interaction of neutrons with
hydrogen atoms. The technique utilizes an Am/Be radioactive sealed source to emit
fast neutrons with high energies through the insulation jacketing.
When these fast neutrons interact with hydrogen atoms, they release energy and are
transformed into slow or thermal neutrons. The thermal neutrons are scattered in all
directions, but have a short travel path. Some of these thermal neutrons are scattered
back toward the scanning head and counted by a sensitive detector.
The more hydrogen atoms present in a material, the more thermal neutrons
produced and counted by the detector.
34
Neutron Backscatter Method:
It should be noted that this technique detects hydrogen atoms,
Therefore, these devices cannot distinguish between water, hydrocarbons, acids,
bases, and organic liquids.
However, the presence of any of these fluids would warrant follow-up inspection,
Effective tool to scan hundreds of feet of insulated pipe to determine wet/saturated
insulation in a short amount of time,
Can help pin-point suspect areas for potential CUI, relatively quick and accurate
method for identifying suspect areas for the potential of CUI,
35
Neutron Backscatter Method:
36
Neutron Backscatter:
Advantages:
•
•
•
•
•
Detects the presence of water or hydrocarbon under insulation jacketing,
Easy-to-use method that can be used to rapidly scan insulated surfaces,
Can access elevated areas without the need of scaffolding,
Lightweight and versatile to reach congested areas,
Effective tool to scan hundreds of feet of insulated pipe to determine wet/saturated
insulation in a short amount of time,
Disadvantages:
• Detects the presence of water or hydrocarbon in the insulation system, not corrosion,
• Technique is only effective while insulation is wet, technique is not effective if
sufficient time has elapsed for insulation to dry out,
37
Thermal / Infrared Imaging Examination
Method
38
39
Thermal / Infrared Imaging Examination Method:
• The thermal/infrared imaging examination method (Thermography) is another
approach for assessing the potential for CUI on insulated vessels and piping,
• Thermography is a rapid, passive inspection technique that produces a Heat-Picture
of the surface of a component using a thermal imaging infrared (IR) camera,
• IR cameras are used to detect Damp-Spots in the insulation due to a temperature
difference between the dry and the wet insulation,
• IR cameras can detect surface temperature variations on the component as small as
0.10°C,
40
• Temperature variations on the component are displayed as different colors,
• Depending on the temperature of the product contained, “hot-spots” or “cold-spots”
on the thermograph show up because of the effect of moisture increasing local
conductivity in the component,
41
Thermal / Infrared Imaging Examination Method:
• Conducting the Thermal / Infrared Imaging Examination IR survey 2 to 3 hours
after the sun-set is advantageous since wet insulation holds the heat absorbed
from solar rays longer than dry insulation. This can tend to promote more contrast
in the thermograph,
• In general, Thermal / Infrared Imaging Inspection for CUI should be done in the
absence of strong gusty winds (non-windy conditions),
• It should be noted that while water may be detected with this technique, it does
not necessarily mean that CUI is occurring,
42
Thermal / Infrared Imaging Examination Method:
Advantages:
• Rapid method to detect damaged or wet insulation,
• Non-invasive, Non-contact method that does not require direct access to the
insulated surface (can be done from ground level without scaffolding),
• Easy-to-use method to highlight areas requiring inspection follow-up,
Disadvantages:
• Does not detect corrosion but only areas where insulation may have been
compromised (damaged or wet insulation),
• Not effective method if insulation has had sufficient time to dry out,
43
Guided Wave Examination Method (GWT)
(Long-Range Ultrasonic Testing)
44
Guided-Wave Examination Method (GWT):
The equipment operates in a pulse-echo configuration where the array of
transducers is used for both the excitation and detection of the signals,
45
Guided-Wave Examination Method (GWT):
• Guided-Waves are a low frequency and long wavelength mechanical wave which
allows a long range of coverage,
• The presence of changes in the pipe cross section due loss of thickness,
circumferential welds, pipe features and others of the same magnitude causes a
reflection of the Guided-Waves,
• This reflection is detected and recorded at the ring of transducers in pulse echo
configuration,
• Each reflector cause a signal in the screen with an amplitude directly proportional
to reflector size and decays with the distance from the ring of transducers,
• Guided-Waves Testing can also provide inspection coverage over long distances
46
under the right circumstances,
Guided-Wave Examination Method (GWT):
47
Guided-Wave Examination Method (GWT):
48
Guided-Wave Examination Method (GWT):
3
6
-18dB
9
Amplitude (arb.)
Amp (Linear)
U2
20.0
S4
B1
10.0
S3
S2
0.0
S1
F1
U1
2.0
-10.0
W4
12
-20.0
W3
Clock position (h)
Clock
12
1.5
1.0
0.5
0.0
-20.0
-10.0
0.0
Distance (m)
Distance
(m)
49
10.0
20.0
Guided-Wave Examination Method (GWT):
• GWT can be used as a screening method to identify potential areas of CUI
damage,
• GWT can be performed without widespread removal of the insulation system (i.e.
jacketing and insulation),
• GWT utilizes an array of low-frequency ultrasonic transducers, attached to the
pipe circumference of a pipe, to generate an axially symmetric wave in both
directions away from the transducer array,
50
51
Guided-Wave Examination Method (GWT):
• Factors that limit the effectiveness of GWT include:
• Excessive internal or external surface roughness,
• Exterior connections such as welded pipe supports, (Inspection coverage is also
limited by the number of welds and elbows in the piping system,)
• High viscosity liquids in the piping,
• Soil in direct contact with the exterior of the piping system,
52
Guided-Wave Examination Method (GWT):
• Defects located in the immediate vicinity of welds are difficult to identify because
of the strong ultrasonic reflection from the weld itself and could be as much as 6
in. (150mm) on either side of the weld,
• This method cannot detect localized pits,
• This method typically requires corrosion damage be greater than 4 % to 10 % of
the pipe cross section to be detected,
• This method of inspection may not be applicable if CUI damage is not extensive,
• In addition to the limitations discussed above, it should be noted that
interpretation of data is operator dependent,
53
Guided-Wave Examination Method (GWT):
• In addition to the limitations discussed above, it should be noted that interpretation
of data is operator dependent,
• Owner/users should review the experience of operators performing GWT on piping
systems prior to conducting an inspection,
• Some owner/users have required performance demonstration tests prior to initiating
an extensive GWT program,
• GWT will identify suspect areas of corrosion in a short period of time, which can
then be proved up with other conventional NDT,
• Detects not only external corrosion but also internal corrosion,
• Can inspect In-Service lines,
54
Guided-Wave Examination Method (GWT) applications:
•
•
•
•
•
•
•
Coated Piping,
Insulated Piping,
Over-Head piping,
Above Ground piping,
Sleeved road cross piping,
Buried piping,
Offshore pipe,
55
Guided-Wave Examination Method (GWT):
Advantages:
• Can inspect up to 100ft (30m) in each direction away from the transducer array,
• Only ~3ft (1m) of insulation need to be removed to attach transducer array,
• Piping from 2” to 48” NPS can be tested,
Disadvantages:
• Limited to applications operating below 125°C,
• Piping containing high-viscosity liquids, heavy external coatings, buried piping, or
piping with an excessive number of welds/fittings can reduce the extent of inspection
coverage,
• Isolated pitting or corrosion in the immediate vicinity of welds may not be detected,
• Technique is operator dependent,
56
Pulsed Eddy Current Method (PEC)
57
Pulsed Eddy Current Method (PEC):
A magnetic field, created by an electrical current in
the probe coil, penetrates the jacketing and
magnetizes the pipe wall. Current, in the probe coil,
is then switched off to cause a sudden drop in the
magnetic field. As a result of the change in the
magnetic field, eddy currents are generated in the
pipe wall. These eddy currents diffuse inward and
decrease in strength. This decrease in the strength
of the generated eddy currents is monitored by the
probe coil. The thickness of the component is
related to the length of time it takes for the eddy
currents to show a change of the decay rate when
eddy currents reach the back wall of the metal. The
greater the wall thickness of the component, the
longer it takes for the eddy currents to reach the
back-wall.
58
Pulsed Eddy Current Method (PEC):
59
Pulsed Eddy Current Method (PEC):
• PEC has been used in recent years to detect areas of wall thinning on
insulated piping through aluminum or stainless steel jacketing,
• It is also used to inspect fireproofed legs on storage spheres,
• It is a noncontact, electromagnetic examination method used to detect the
average wall loss of carbon and low alloy steel materials,
• PEC can be used on carbon and low alloy steel equipment and piping
through up to 8 in. (200mm) of insulation and jacketing,
60
Pulsed Eddy Current Method (PEC):
61
Pulsed Eddy Current Method (PEC):
• The area where the measurement is taken is referred to as the “footprint”,
• The probe is designed in such a way that the magnetic field focuses on an area on
the surface of the component,
• The thickness measured by the technique is the Average Wall Thickness “AWT”
over the footprint area,
• The size of the area is dependent on the insulation, component thickness, and probe
design,
• In general, the footprint can be considered to be on the order of the insulation
thickness,
• Since the technique measures the average rather than the minimum component
thickness, the technique is not suitable to detect pitting that can be highly localized,
62
Pulsed Eddy Current Method (PEC):
Difference Between Average and Minimum Wall Thickness Within the Footprint
63
64
Pulsed Eddy Current Method (PEC):
Advantages:
• Non-invasive, Non-contact method that does not require surface preparation,
• Can be used between –100°C and 500°C,
Disadvantages:
• Averages corrosion over a 4in. (100mm) diameter area so that isolated pitting may
be difficult to detect,
• Affected by ferromagnetic appurtenances such as insulation rings, vents, and drains
that can obscure surface damage,
• Technique is operator dependent,
65
Radiographic Inspection Methods
66
Radiographic Inspection Methods:
• There are a variety of techniques involving radiographic methods that can be used to
detect CUI damage,
• Radiography essentially requires a source of radiation opposite a detection medium
that records the radiation either as a film or digital image, these include:
• Tangential Radiographic Inspection (Profile Radiography),
•
•
•
•
•
Double Wall Radiographic Inspection (Film Density Measurement Technique),
Real-time radiography,
Computed radiography (CR),
Digital radiography (DR),
Radiometric profiling,
67
Radiographic Inspection Methods:
• Radiographic Examination is a very effective method that can be used for the
Inspection of CUI,
• Unlike other methods, Radiography cannot only find CUI but also produce
accurate wall lose measurements without insulation removal,
• Can be utilized while Pipe/Equipment is in-service,
68
Tangential Radiographic Inspection
(Profile Radiography)
69
Tangential Radiographic Inspection:
70
Tangential Radiographic Inspection:
1. Radiation source located on the pipe center-line,
2. Radiation source located offset from the pipe center-line,
71
Tangential Radiographic Inspection:
• The beam of radiation shall be directed at
the center of the area being examined,
• The film or detector should be aligned to
be orthogonal to the center of the
radiation beam,
• The choice of radiation source should be
determined by the maximum penetrated
thickness of the pipe, 𝒘𝒎𝒂𝒙 which occurs
for the path forming a tangent to the pipe
inner diameter,
72
Tangential Radiographic Inspection:
• “Tangential Radiographic Inspection” is used to radiograph a small section of the pipe wall,
• “Tangential Radiographic Inspection” can also be done using sealed sources or x-ray machines,
73
Tangential Radiographic Inspection:
74
Tangential Radiographic Inspection:
Dimensional comparator:
For measurement of remaining wall thickness,
the film radiographs or digital images shall be
dimensionally calibrated to correct for the
geometric magnification caused by the
geometrical arrangement of source, pipe and
detector.
One method for dimensional calibration is the
use of a ball bearing or other dimensional
comparator. This is an effectively radiation
opaque object (usually spherical) with a known
diameter, which is placed close to the pipe, and
in the same plane as the tangent position on the
pipe wall,
75
Tangential Radiographic Inspection:
For offset tangential radiography (with x
approximately r), the true wall thickness 𝒕𝒂𝒄𝒕
at the tangential pipe position can be
calculated from the measured wall thickness
𝒕𝒎𝒆𝒂𝒔 using the approximate formula:
76
Tangential Radiographic Inspection:
Provided x approximately 0, then the
following complex formula can be used to
derive the wall thickness 𝑡𝑎𝑐𝑡 , from the
measured value 𝑡𝑚𝑒𝑎𝑠 :
𝑤ℎ𝑒𝑟𝑒:
𝑟=
𝐷𝑒
2
77
Tangential Radiographic Inspection:
The source is put far from the tube in order
to project the two walls of this tube on the
film,
Because of dimensions of the radioactive
source,
an
effect
of
Geometric
Unsharpeness appears on the film,
78
Tangential Radiographic Inspection:
Angle of rotation of tangential point:
𝐾=
𝐶𝑜𝑠 −1
𝑟
(
)
𝑓 −𝑅
For optimized results, the source to sensor
distance should be as large as practical, ratio of
source to sensor distance to outside diameter of
6 or more produce low unsharpness values,
High-contrast and Fine-grained films
produce more accurate results when developed
to medium range film optical densities around
2.0,
79
Tangential Radiographic Inspection:
80
Tangential Radiographic Inspection:
• “Tangential Radiographic Inspection” is an effective evaluation method but becomes
technically challenging in piping systems over 10” in diameter and only offers the limited
luxury of verifying relatively small areas,
• This technique is not capable of detecting ECSCC on austenitic or duplex stainless steels,
• Radiation safety can be a real concern, the need to cordon off a large area for radiographic
examination can result in downtime and personnel scheduling conflicts,
• “Tangential Radiographic Inspection” is usually preferred to assess insulated piping for
uniform corrosion damage,
• Great tool for Inspection at Suspect Areas of CUI,
• Can take Profile at multiple different angles to catch Area of interest,
81
Tangential Radiographic Inspection:
Advantages:
• Provides a permanent record of examined areas,
• Provides a relatively easy scanning method without the need for insulation removal,
• Used routinely on piping 2” NPS and above,
• Determines wall thickness with an accuracy smaller than ±1 mm,
• Not only a Screening Tool but can also Produce Accurate Measurements of Wall Loss,
Disadvantages:
• Limitations on pipe size that can be inspected,
• Piping or equipment would require insulation to protect the film at elevated
temperatures,
82
Tangential Radiographic Inspection:
83
Film Density Measurement Technique
(Double Wall Radiographic Inspection)
84
Film Density Measurement Technique:
85
Film Density Measurement Technique:
• Tangential Radiographic Inspection and Film Density Measurement Technique
are complementary methods,
• Film Density Measurement Technique is preferred to assess pitting corrosion
damage on insulated piping because of the difficulty of aligning pits
perpendicular to the radiographic beam in profile radiography,
• Film Density Measurement Technique only measures the Average Wall Thickness
(AWT) of the piping and is often used on small diameter piping [≤6”] however,
with some trade-offs, this technique can be used on larger diameter piping,
• The appropriate energy and appropriate film speed should be chosen when the
Film Density Measurement Technique is utilized to achieve good image quality,
86
Film Density Measurement Technique:
• Part 2 of EN-16407 covers “Double Wall Inspection Techniques” for detection of wall loss,
including double wall single image (DWSI) and double wall double image (DWDI),
• The “Double Wall Radiographic Techniques” are divided into two classes:
1) Basic Techniques “DWA”:
The “ Basic Techniques” are intended for double wall radiography of generalized and
localized wall loss,
2) Improved Techniques “DWB”:
The “Improved Techniques” should be used where higher sensitivity is required such as
for radiography of fine, localized corrosion pitting,
• These techniques can also be used for detection of deposits inside the pipe,
87
Film Density Measurement Technique:
Test arrangement for double wall single image radiography (DWSI) using a curved detector,
Non insulated pipe
insulated pipe
88
Film Density Measurement Technique:
Test arrangement for double wall single image radiography (DWSI) using a planar detector,
Non insulated pipe
89
insulated pipe
Film Density Measurement Technique:
Test arrangement for double wall double image radiography (DWDI),
Non insulated pipe
insulated pipe
90
Measurement of differences in penetrated thickness:
To a first approximation, the radiation intensity transmitted through an object is related to penetrated
thickness by:
I(w) = I(0) exp(-μ w)
Where:
I(w)
is the intensity for penetrated thickness w,
I(0)
is the unimpeded radiation intensity incident on the object,
μ
is the effective linear attenuation coefficient of the object material,
Consider two different penetrated thickness values 𝑤1 and 𝑤2 , Assuming equal incident radiation
intensities and attenuation coefficients for these two penetrated thickness values, application of above
Formula then gives:
1
µ
𝑤2 − 𝑤1 = Ln (
𝐼(𝑤1 )
)
𝐼(𝑤2 )
The ratio of radiation intensities in film radiography shall be determined from the measured optical
densities by the following formula:
𝐼(𝑤1 )
𝐼(𝑤2 )
=
Where: 𝐷0 is the optical density of film base and fog.
91
𝐷1 −𝐷0
𝐷2 −𝐷0
Film Density Measurement Technique:
• The density/thickness reference curve should
be developed using step wedges that are made
from material that is radiographically similar
to the piping being evaluated,
• The step wedge thickness should be twice the
thickness of the pipe wall being evaluated,
92
Film Density Measurement Technique:
• It is important to locate the pit or local corrosion area correctly, The pitting should
lie on film side during exposure to prevent an underestimation of its depth,
• The depth of the pitting and remaining wall thickness can be determined using the
measured optical density of the pit and sound wall and a density/thickness
reference curve,
93
Film Density Measurement Technique:
Advantages:
• Provides a permanent record of examined areas,
• Provides a relatively easy scanning method without the need for insulation removal,
• Technique can locate irregular or scattered pits,
Disadvantages:
• Corrosion products within pits can decrease film density and result in an incorrect
determination of the wall thickness,
• Liquids present in the equipment (piping) will reduce the transmitted radiation,
• An ultrasonic examination will also be required if density curves are not calculated,
• Piping or equipment would require insulation to protect the film at elevated
temperatures,
94
Related Standards:
BS-EN 16407-1 (2014)
Non-destructive testing, Radiographic inspection of corrosion and deposits in
pipes by X and gamma rays
Part (1): Tangential Radiographic Inspection
BS-EN 16407-2 (2014)
Non-destructive testing, Radiographic inspection of corrosion and deposits in
pipes by X and gamma rays
Part (2): Double Wall Radiographic Inspection
95
Computed Radiography (CR)
and
Digital Radiography (DR)
96
Computed Radiography and Digital Radiography:
• Film radiography is the dominant, volumetric nondestructive testing technique used
throughout the world,
• The primary advantages of film radiography are that film is:
• Lightweight,
• Flexible,
• Used in a variety of applications for many years with a proven track record,
• Despite this, film does have disadvantages:
•
•
•
•
•
Film processing requires significant amounts of time to develop radiographs (~20 min),
Specialized facilities for film processing (i.e. a darkroom),
Generates hazardous wastes that require disposal,
Film radiographs have a limited shelf life,
Require a temperature and humidity-controlled storage environment,
97
Computed and Digital Radiography:
By contrast:
1. DR requires none of the above,
2. CR requires less exposure time, and no need to chemicals,
3. Digital Images can be generated, optimized, analyzed,
stored, and distributed in electronic format,
98
Computed Radiography (CR):
99
Computed Radiography (CR):
• CR is a transitional technology between film and direct DR.
• A re-usable, flexible, Phosphor Image Plate is loaded into a cassette and is
exposed in a manner similar to traditional film radiography. The cassette is then
placed in a laser reader where it is scanned and translated into a digital image,
• Depending on the resolution required and image size, the process of digitizing
may take from 1 minute to 5 minutes,
• Once digitally captured, the image may be stored on a computer or other
electronic media,
• Archiving is made easier and the images can be electronically distributed to
others for viewing,
100
Computed Radiography (CR):
101
102
Computed Radiography (CR):
Advantages:
•
•
•
•
•
No silver based film or chemicals are required to process film,
Reduced film storage costs because images can be stored digitally,
Requires fewer retakes due to underexposure or overexposure,
Images can easily be stored and electronically distributed to others,
Produces a sharper image than conventional film in less time 1-5min vs 10-20 min,
Disadvantages:
• Imaging plates can be damaged by rough handling,
103
Computed Radiography (CR):
104
Computed Radiography (CR):
105
Computed Radiography (CR) Using the Wall Thickness Tool:
106
Computed Radiography (CR) Exposure time:
107
Digital Radiography (DR)
108
Digital Radiography (DR):
109
Digital Radiography (DR):
A direct DR system is different from CR in that it digitizes the photon radiation that
passes through an object directly into an image that can be displayed on a computer
monitor,
There are three technologies used in direct digital imaging systems:
1. Amorphous Silicon Devices,
2. Charge Coupled Devices (CCD),
3. Complementary Metal Oxide Semiconductor Devices (CMOS),
Direct digital system images are available for viewing and analysis in seconds as
compared to the minutes required in CR systems,
110
Digital Radiography (DR):
• The increased processing speed is a result of the unique construction of the pixels
in a direct digital system,
• The pixels arrangement that also allows an image resolution that is superior to CR
and most film applications,
• Produces Superior Quality to other RT forms in a shorter time can produce an
image within seconds,
• Less radiation needed to produce image compared to Film RT,
• Requires a computer, monitor and cables for immediate viewing of image,
111
Digital Radiography (DR):
Advantages:
• Requires less radiation to produce an image compared to film radiography,
• The image may be stored, emailed, or processed on a computer,
• Automated Defect Recognition (ADR) systems can be used to analyze the image,
replacing the subjective assessment of an inspector,
Disadvantages:
• DR panel detectors require care to avoid damage,
• Lifetime of DR panel detectors dependent on duty cycle / doses applied,
• As a result of manufacturing, every DR panel has some dead pixels,
112
113
Real-Time Radiographic Examination
Method (RTR)
114
Real-Time Radiographic Examination Method (RTR)
• Real-Time Radiographic Examination Method (RTR), commonly referred to as
fluoroscopy,
• Provides a clear view of the pipe’s OD through the insulation, producing a
silhouette of the OD of the pipe on a monitor that is viewed during the inspection,
• No film is used or developed,
• The Real-Time device has a radiation source and image intensifier/detector that
are connected to a C-arm,
115
Real-Time Radiographic Examination Method (RTR)
• There are two categories of real-time radiography devices:
• One using an x-ray source as radiation source,
• One using a radioactive isotope (i.e. Gd-153) as radiation source,
• Each has its own advantages and disadvantages; however, the x-ray systems deliver
far better resolution than the isotope systems,
116
Real-Time Radiographic Examination Method (RTR)
Binding wire holding insulation in place
Weld Location
Corrosion Under Insulation
117
Real-Time Radiographic Examination Method (RTR):
• The x-ray digital fluoroscopy equipment operates using a low-level radiation source
(≤75 KV),
• The equipment allows the kV and/or mA of the x-ray tube to be adjusted to obtain
the clearest image and allows for safe operation without disruption in operating
units or even confined spaces,
• As a result of the low-level radiation, the radiation does not penetrate the pipe wall,
• Instead, the radiation penetrates the insulation, and images the profile of the outer
wall of the pipe,
118
Real-Time Radiographic Examination Method (RTR):
• In order for CUI to be detected on insulated pipe, it may be necessary to rotate the
fluoroscopy device 360° around a pipe,
• In many instances, the image may indicate a rough surface of the OD of the pipe
indicative of corrosion; however, other means should be employed to determine the
extent or degree of corrosion present,
119
Real-Time Radiographic Examination Method (RTR):
• Since the radiation is generated electrically, the instrument is perfectly safe when the
power is off,
• Equipment utilizing radioactive material requires additional precautions to ensure the
source is shielded when not being used, These precautions extend to transportation
and storage of radioactive material in accordance with state mandated regulations,
120
Real-Time Radiographic Examination Method (RTR):
• Most of the fluoroscopy systems come with a heads-up video display,
• A helmet-mounted, visor-type video display frees the system operator’s hands to
maneuver the C-arm while keeping the image before the operator at all times,
• The heads-up display also improves interpretation by shielding the screen from
the sun.
121
Real-Time Radiographic Examination Method (RTR):
Advantages:
• Images are easily viewed because they are digital and can be electronically stored
and retrieved using a computer,
• There is no maximum size limitation since multiple arrays can be assembled to
view large areas,
Disadvantages:
• Adequate clearance [i.e. 30cm] required on piping in congested areas,
• Wet insulation hampers testing,
• Radioisotope system’s image quality deteriorates as isotope decays,
122
Advancements
in
Portable Real Time
Corrosion Under Insulation
(CUI)
Inspection Instrument
123
External Corrosion
Inspection
124
Dimensions (x-ray tube to imager):
Standard:
Adjustable to 19 in (48.26 cm)
Extended:
Adjustable to 25 in (63.5 cm)
125
X-ray Energy and Intensity:
• High
• Medium
• Low
70kV / 0.3mA
70kV / 0.1mA
40kV / 0.1mA
Live Imaging (Detector’s Specification):
• Imaging Area:
• Spatial Resolution:
4” x 6” (10cm x 15cm)
250µm
126
127
128
Specification:
•
•
•
•
•
•
•
•
•
•
Compact Size,
Light weight,
Adaptable,
Ergonomic (comfort design and user-friendly system),
Fast Real-Time Inspection,
Good Resolution,
Adjustable Power Ranges (kV and mA),
Low Dose to Operator,
Battery Operated,
Durable,
129
Single Battery Operation:
•
•
•
•
•
•
28 volts lithium-ion (max power density),
State of Charge Indicator,
40 minutes continuous x-ray on,
4 hours typical use,
One hour recharge,
Readily available,
130
Display:
1 - 6.5” (16.51 cm) Hand Held LCD viewer,
2 - Ruggedized Head Mounted Display (HMD),
131
Recording:
• Digital Video Recorder/Display with 4GB SD card,
• 3.5” Visual image, x-ray image TFT LCD Display
(Thin-Film-Transistor Liquid-Crystal Display)
• 4 hours on removable 4GB SD card,
• Wireless System,
• wmv Format,
132
Light-weight & Ergonomic:
C-arm with x-ray tube & imager: 5.7kg
Controller including large battery and shoulder strap: 1.5kg
Durable:
Over 10,000 weld packs inspected
on Alaska’s North Slope with one system,
Operating Temperature:
-29ºC to +49ºC
133
Packaging:
All components housed in a wheeled field case:
• Shipping weight:
• Case size:
24 kg
82cm x 52cm x 32cm
134
Conclusion:
RTR-CUI as a real-time video x-ray system is
available for NDT applications, especially
useful for Corrosion Under Insulation surveys
(CUI) and weld location,
135
Radiometric Profiling Technique
(Pipe Profiler)
136
Radiometric Profiling Technique:
• These handheld radiographic systems use a gadolinium 153 radioactive source in
combination with a solid state scintillator that converts γ-rays into photons,
• The activity of the source and the length of the C-arm used determine the
maximum density that the equipment can penetrate when looking for CUI,
• This equipment can allow estimation of the pipe wall thickness when shot through
the center of the pipe,
• In general, this equipment is capable of inspecting insulated standard wall
thickness pipe with an overall OD of up to 18”,
137
Radiometric Profiling Technique:
The limitations with regard to pipe and insulation diameter depends on:
• The product inside the pipe,
• The density of the pipe material (thickness),
• The type of insulation,
• The type of insulation jacketing being penetrated,
138
Radiometric Profiling:
Advantages:
• Suitable for piping from ½” to 18” NPS,
• No radiation barricade is required to utilize device,
• Portable and may be operated by a single technician,
Disadvantages:
• Measures the remaining combined double-wall thickness, not the pipe wall thickness
of the corroded area,
• Cannot differentiate between ID and OD corrosion,
• Requires a radioactive materials license,
139
Radiometric Profiling Technique:
140
Radiometric Profiling Technique:
The Pipe Profiler is comprised of:
•
•
•
•
A very low activity gamma radiation source (Gd-153),
A solid state scintillator photon detector,
Three arms 6”, 13” and 18”,
A computer to translate the density of the piping system under test to a relative
numerical thickness value,
141
Physical Characteristics of Gd-153:
Half Life:
Type Decay:
Gamma Rays:
• Beta Rays:
241.6 days
e- capture
0.041 MeV (35.8 %)
0.042 MeV (64.7 %)
0.047 MeV (25.3 %)
0.070 MeV (2.57 %)
0.084 MeV (0.22 %)
0.097 MeV (31.3 %)
0.103 MeV (22.2 %)
0.103 MeV Maximum
142
Radiometric Profiling Technique:
• The Pipe Profiler is a measurement tool that has been developed to help identify
the most deteriorated areas of piping systems in a rapid and economical manner
in order to ensure the integrity of a great majority of industrial piping,
• The Pile Profiler is designed to be a portable, rapid scanning tool for piping
systems in order to detect many of defects,
• The Pipe Profiler will report the results in the form of a line graph of thickness,
143
Radiometric Profiling Technique:
The system is easily calibrated utilizing three known thickness values.
144
Radiometric Profiling Technique:
145
Radiometric Profiling Technique:
146
Radiometric Profiling Technique:
Subsequent scanning of piping will reveal the presence of density variations caused by:
•
•
•
•
•
•
•
Internal Corrosion,
External Corrosion,
Erosion,
Welds location,
Wet insulation,
Product buildup on the walls of the pipe,
Any other cause for density changes,
147
Radiometric Profiling Technique:
• The portability of the Pipe Profiler is because of the use of Gd-153 limited to a
maximum value of 1Ci,
• The Pipe Profiler also limited to penetrating a maximum of 2” of steel with a new
source, and an average of 1.5”of steel or steel equivalent for the remaining useful
life of the source,
• Fortunately, most of the piping systems utilized in industrial and process
environments fall well within the range of operability for the Pipe Profiler to be
utilized in an effective and economical fashion for the inspection of these piping
systems,
148
Radiometric Profiling Technique:
If the beam of the radiation is not centered along the diameter of the pipe, the
thickness values will increase due to chord length effects,
This fact may seem obvious at first, but when inspecting insulated pipe, the
insulation jacket is not always oriented concentrically to the pipe underneath and
the radiation beam will not be passing through the pipe coincidentally with the true
diameter of the pipe. This may result in higher than actual thickness values,
149
Radiometric Profiling Test Procedure:
The Pipe Profiler is operated in 2 distinct ways:
1. To “axial scan” along the length of the pipe,
2. To “slice scan” through the pipe at 90 degrees,
150
Radiometric Profiling Test Procedure:
Axial scans are carried out at various orientations (primarily at 6 / 12 O’clock),
depending on the pipe process, corrosion expectations and inspection requirements,
151
Radiometric Profiling Test Procedure:
Slices scans can also be taken at different angles to help clarify areas of concern,
152
Applications of Radiometric Profiling Technique :
•
•
•
•
•
•
•
•
•
•
Wall thickness measurement on insulated or bare pipes with or without product,
Wall thickness measurement on very hot pipes while in service,
Pipe wall thinning,
Detection of internal & external corrosion,
Detecting of Pipe blockages,
Detecting water and ice in insulation,
Detecting of cluster of internal and external pitting,
Weld identification on insulated piping systems,
Assessing product levels,
Can be used to ensure that valves are open and lines are clear,
153
Benefits of the Radiometric Profiling Technique:
•
•
•
•
•
•
•
•
•
•
•
•
•
Fast: No surface preparation,
Safe: Low dose radiation (1Ci of Gd-153) therefore, No need to rope off an area while testing,
Instant: Real-Time results (on site reporting),
Contactless: No contact is needed with piping therefore can be used on high temperature pipes,
The entire pipeline can be scanned rather than a spot measurement,
Complete (100% coverage) inspection,
Can be used on metallic and non-metallic piping,
Compared to other NDT techniques, is very rapid and allows for much more pipe to be
inspected in a given day,
Quick Analysis,
Lightweight & battery operated allows Hand-Held, easy to move,
Easy to use and easy operation device,
Lower inspection cost,
Reduce Downtime,
154
Limitation of the Radiometric Profiling Technique:
•
•
•
•
•
•
Maximum diameter piping of 18” (external),
Maximum pipe wall thickness of 25mm (1”),
Access is needed on both sides of the pipe for the C-arm,
Not recommended for detection of pinholes / cracks,
Extensive training and experience necessary for operation and data interpretation,
Accurate information required from client to allow adequate calculations,
155
Pipe Size
Wall Thickness
Couplant
Up to 18” including Insulation
Up to 25mm
None
Surface Preparation
Material
Temperature Range of Pipe
Sensitivity
None
All
All
Greater than 1mm
C-arm Size,
Isotope
Inspection Time
6”, 13” and 18”
Gadolinium 153 (1Ci)
20m to 150m a day
156
Pipe Profiler
This is what an
Axial Scan
would look like of this
section of pipe.
Nominal Wall Thickness
These are the same indications
located on the side of the pipe.
Only the indications on the bottom
(or top) of the pipe would be
detected with a vertical radiation
beam.
The Profiler will only detect
anomalies that are in-line with the
radiation beam
Axial Scan
of insulated
piping with
internal corrosion
Real-time
Profiler results of
axial scan
Corroded
Area
Left:
Profiler oriented perpendicularly over
weld. Response is single, high-amplitude
peak.
Right:
Profiler oriented at an angle while
scanning over weld. Result-baseline
thickness increases and two lower
amplitude peaks result:
one when the detector crosses the top of
the weld and one when the source
crosses the bottom of the weld.
B
A
B
Non-Corroded Side
(More Dense)
A
Corroded Side
(Less Dense)
Center of Pipe
(this is not zero
thickness)
Corrosion on Side of Pipe
T262 : 0 Min / 0.828 Max / 0.447 Avg / 0.398 at Tag : Threshold = 0.281
Slice Values: 0.398 / 0.398 / 0.398 : Session # 291
0.900
Non-Corroded Side
0.800
0.700
Corroded Side
0.600
0.500
0.400
0.300
0.200
0.100
0.000
T
128
Radiation
Beam
134
T
138
136
142
140
146
144
150
148
152
154 T262 162
166
170
174
T262 160
164
168
172
176
Corrosion on Side of Pipe
A
B
C
T262 : 0 Min / 0.828 Max / 0.447 Avg / 0.398 at Tag : Threshold = 0.281
Slice Values: 0.398 / 0.398 / 0.398 : Session # 291
0.900
Non-Corroded Side
0.800
0.700
Corroded Side
0.600
0.500
0.400
0.300
A
0.200
B
C
0.100
0.000
T
128
134
T
138
136
142
140
146
144
150
148
152
154 T262 162
166
170
174
T262 160
164
168
172
176
With a Slice Scan, corrosion on the side of the pipe can be
detected even though the radiation beam is not perpendicular
to the axis of the pipe. If detected, a second slice scan should
be performed at a right angle to the first slice scan.
`
Area of No
Sludge
The slice scan on the left
is through the section of
pipe free from debris.
The slice scan on the right
is through a section of
pipe having debris in it.
Welds
Thick wall pipe
Thin wall pipe
Medium wall pipe
Reducer
Weld
Detecting
Pipe Schedule
Changes
Sch. 80
Sch. 40
Heat Affected Zone
Corrosion (HAZ)
Weld
Blockage
Ice/Water in the
insulation
Ice
Dry Insulation
Water
Dry vs. Wet Insulation
T125 : 0 Min / 0.553 Max / 0.313 Avg / 0.377 at Tag : Threshold = 0.281
Slice Values: 0.377 / 0.377 / 0.377 : Session # 13
0.600
A B C
0.500
0.400
Dry
0.300
A
0.200
B
C
0.100
0.000
T
143
T
T
148
T
150
149
152
151
153
154
T125 T125
160
162
164
166
168
T125 T125
159
161
163
165
167
169
T219 : 0 Min / 0.845 Max / 0.401 Avg / 0.679 at Tag : Threshold = 0.281
Slice Values: 0.447 / 0.679 / 0.679 : Session # 279
0.900
A B C D E
0.800
0.700
A
0.600
0.500
B
C
D
E
Ice/Water
0.400
0.300
The “thickness” of the pipe center
increased due to the density
contribution of the Ice/Water
0.200
0.100
0.000
T
42
48
T
52
50
56
54
60
58
64
62
T219
72
76
80
84
88
T219
70
74
78
82
86
Perpendicular
scan of weld
Nominal
Baseline
Angled
Baseline
Angled scan
of weld
Erosion
Weld
Weld
Elbow
Horizontal
Pipe
Vertical
Pipe
Typical Erosion Detection
Typical Level Gauging
Summary:
• Have a Plan for CUI Inspections If you Fail to Plan you Plan to Fail,
• Choose Inspection Methods Accordingly,
• Be proactive, don’t wait for a CUI failure to spark your inspections,
IT MAY BE TOO LATE!!
176
References:
1.
API-RP583 (2014), “Corrosion Under Insulation and Fireproofing” American Petroleum
Institute (API) Recommended Practice 583 First Edition, May 2014,
2.
“ASNT Nondestructive Testing Handbook” Third Edition: Volume 4, Radiographic Testing
(RT), Third Edition,
3.
“Radiographic Evaluation of Corrosion and Deposits in Pipelines: Results of an IAEA Coordinated Research Program” ECNDT 2006 ,Uwe ZSCHERPEL, Uwe EWERT, BAM,
Berlin, Germany Silvia INFANZON, AENDUR, Montevideo, Uruguay Nasser RASTKHAN,
Atomic Energy Organization of Iran, Teheran P. R. VAIDYA, Bhabha Atomic Research
Centre, Mumbai, India Isaac EINAV, IAEA, Vienna, Austria Sinasi EKINCI, Turkish Atomic
Energy Authority, Istanbul, Turkey,
4.
BS-EN 16407-1 (2014), Non-destructive testing, Radiographic inspection of corrosion and
deposits in pipes by X and gamma rays, Part (1): Tangential Radiographic Inspection,
5.
BS-EN 16407-2 (2014), Non-destructive testing, Radiographic inspection of corrosion and
deposits in pipes by X and gamma rays, Part (2): Double Wall Radiographic Inspection,
177
178
179